## How Oximeter measures Pulse Rate & Oxygen level in your Blood

A Pulse Oximeter is as small clip like device that measures pulse rate & oxygen level (SPO2) in your blood by non-invasive method .

You should know that a normal resting pulse rate is in between 60 to 100 BPM (beats per minute) and normal oxygen level (SPO2) between 95% to 100% .

As we know that we need oxygen for survival . Oxygen enter our lungs and pass on into the blood . The way oxygen is carried in our blood by means of Hemoglobin . The Hemoglobin (Hb) with oxygen called “ oxy Hb “ and without oxygen called “deoxy Hb” . Oxy Hb and deoxy Hb absorbs infrared & red light differently . Oxy Hb absorb more infrared light and deoxy Hb will absorb more red light .

How it Works :

A pulse oximeter uses a pair of light (infrared & red) of high intensity from LED (Light Emitting Diode)to measure oxygen saturation level in your blood .

The device has a light source and light detector . If a finger is placed between light source and detector , the light has to pass through the finger to reach the detector .

According to law in Physics “The amount of light absorbed is proportional to the concentration of light absorbing substance ” .

As Hemoglobin (Hb) absorbs light . “The amount of light absorbed is proportional to concentration of Hb in blood vessel “ .

As Oximeter detects how much light has been absorbed and how much reaches the detector . In this way oximeter measures the oxygen level in the blood .

In covid-19 pandemic everyone should keep pulse oximeter in his house . This device is small & also not so costly . You may purchase it from any medical store or online store .

## How Video game can improve your memory and Concentration

As we all know that gaming is essential for physical & mental fitness .

In this article we are talking about brain train game . The question arises  always in our mind that , can brain train game improves our memory & Concentration ? The answer is Yes .

It has to be found by study that brain train game improves short term memory , long term memory , response time and logical thinking skills .If a person would like to give workout to his brain , it may improve mental focus & fitness . It has to be found by neurobiologist in his study gaming can improve memory test score . In his study on two groups playing video games , one group that played in 2-D environment and other in 3-D environment . After playing 30 minutes per day for two weeks , the participants were given memory test , the participants those in 3-D group significantly improve their memory test score as compared to 2-D group . There are many games by which you may improve your skills such as reading , writing , speaking etc. You may also customize according to your choice and also track your progress to see how your skills are improving .

### CHESS :

If you want to improve your memory & concentration consider all time classic “CHESS” . It has to be found by study that regular CHESS player or expert have better memory & concentration . You may also serve social activity by playing Chess with your friend , family & colleague .

In other way you may also prefer to play on your Mobile Phones , tablets or PC .  In this way it will provide you virtual Competitors and you can challenge your mind . Playing more focussed chess also improves your logical thinking .

### VIDEO GAME:

Video games are another better options for improving memory & concentration . It has to be found by study that video games which are based on playing & skillful thinking helps to improve the brain function .

Video game can also bridge the gap between adult & children by playing game together and also builds up deeper relationships . It has to be found that video game player also improves their several types of attention such as sustained attention , selective attention etc.

RELIEF PHYSICAL PAIN  :  It has to be found by study that video game may also relief physical & mental pain . Patient get relief from pain by engaging themselves with video game .

REDUCING DEPRESSION & STRESS : Video game may also helps in reducing stress for those students who suffering  from depression & stress .

IMPROVE DECISION MAKING CAPACITY : On playing games , gamer has to take second decision at a certain instant of time by doing this he can improve their decision making capability .

“  One should always keep in mind that games are for Refreshment for their mind , body & soul “

## Thermal Equilibrium and Temperature

HEAT AND THERMODYNAMICS
Content : Thermal Equilibrium and Temperature (Zeroth law of Thermodynamics) , Macroscope & Microscopic Descriptions

In analyzing physical situation we usually focus our attention on some portion of matter which we separate, in our minds, from the environment external to it. We call such a portion the system. Everything outside the system which has a direct influence on its behaviour we call the environment

Example – A ball can be the system and the environment can be the air & the earth. In free fall, we seek to find how the air and earth affect the motion of the ball.

In all such cases we much choose suitable observable quantities to describe the behaviour of the system. We classify these quantities as Macroscopic (like pressure, volume, temperature for example) and Microscopic (Here, we consider quantities that describe the atoms and molecules that makeup the system, their speeds, energies, masses, angular momenta, behaviour during collisions, etc.)  Thus macroscopic quantities form the basis of science of thermodynamics. While the microscopic quantities form the basis of science of statistical mechanics.

Thus for any system, the microscopic and macroscopic quantities must be related because they are simply different wrap of describing the same situation.

Example : Let us take open tube mercury monometer connected to a gas tank, the pressure of a gas viewed macroscopically, is measured using a manometer. If it is viewed microscopically it is related to the average rate per unit area at which the molecules of the gas deliver momentum to the manometer fluid as they strike its surface

Thermal Equilibrium (The Zeroth law of Thermodynamics)

Let us consider an object A which feels cold to the hand and identical object B which feels hot and let both be placed in contact with each other. After a sufficient length of time, A and give rise to the same temperature sensation. Thus A and B are said to be in thermal equilibrium with each other.

We can generalize the expression : Two bodies are in thermal equilibrium, to mean that the two bodies are in states such that if the two are connected, the combined system would be in thermal Equilibrium. The logical test for thermal equilibrium is to use a third body such as a thermometer. This is summanized in a law called “the zeroth law of the thermodynamics”

STATEMENT : If A and B, two objects are in thermal equilibrium with a third body C (The ‘Thermometer’)s then A and B are in thermal equilibrium with each other.

Thus, a scalar quantity, temperature, which is a property of all thermodynamic systems (in equilibrium states), such that any two systems having the same temperature must be in thermal equilibrium with each other
Example :- If shows two system A and B separated by an adiabatic wall (a wall which does not allow heat flow)

The two systems are placed together with third system C with a diathermic wall (a wall which permits heat flow) in between. Suppose A, B, C are at different temperatures. Systems A & C, B & C will be exchanging heat with each other, after certain length of time, they will attain thermal equilibrium with each other separately. It the adiabatic wall is removed between A and B at that time, it will be found there will be no exchange of heat between  the systems A and B. Therefore, the system A and B are allowed to attain thermal equilibrium separately with the system C.

Temperature : The degree of  hotness of a body is called its temperature.

As we know that bodily sensation of warmth and cold is not reliable. Suppose we place our right     hand in hot water and the left hand in cold water. If after a few minutes, we place our both the hands in water at room temperature it will be found that to the right hand, the water will appear cold, while   to the left hand the same water will appear hot. Hence our judgment of temperature can be rather     misleading. Further, the range of our temperature sense is limited. What we need is an objective, numerical, measure of temperature.

An instrument used to measure the tempearture of a body is called a thermometer .
HEAT When two systems at different temperatures are placed together, the final temperature reached is in between the two starting temperature. This has a common observation upto the beginning of the nineteenth century, it was considered that a material substance ‘Caloric’ existed in every body. It was believed that a body at high temperature contained more caloric than one at a lower temperature. This caloric is nothing but heat, which is transferred between a system and its surroundings as a  result of temperature difference only.

###### ♠ Heat is a form of energy which produces in us the sensation of warmth.

Example : a piece of burning charcoal is known to be very hot, while Ice cube is very cold.

When bodies are heated, physical changes are likely to develop like change of state, (from solid to liquid incase of ice cube) expansion, (on heating gas expands as molecules have more kinetic energy), contraction etc.

Heat is a form of energy. For example, when we heat the gas in a container by burner it expands as the kinetic energy of the molecules increases due to heat imported to it which causes expansion. Hence, Heat energy is converted into kinetic energy which is nothing but mechanical energy. Thus, energy can be changed from one form to another form.

In 1978, Count Rumford engaged in making a bore in the brass cannon observed that the drilling tool became hot. Also, the brass chips cut off from the barrel of the cannon produced a sufficient increase in the temperature of the water on following in it (to prevent over heating, the bore of the cannon was kept full of water). The water was replenished as it boiled away during the boring process. In order to explain the production of heat during the drilling process, according to early caloric theory, when a metal cut into fine chips, the heat squeeze out from the body. It implied that the heat of the metal is the form of chips less than its value, when it is in the form of block. However, experiments conducted by Rumford proved that there is no difference in the values of specific heat of metal in two cases. It led to the downfall of caloric theory

## Electromagnets & Permanent magnets

### Electromagnets

They are normally used for the purpose of lifting ferromagnetic substance.

Properties of the material of an electromagnet :

(1)  The material should have low retentivity so that it gets demagnetised easily.

(2)  For the electromagnet to be very strong, it should have a high value of saturation magnetisation.

(3)  It should have low coercivity .

(4)  Hysteresis loss should be small. It should not be heated up during magnetisation and demagnetisation.

The above-mentioned properties are reasonably met with soft iron and so soft iron is usually preferred for an electromagnet.

### Permanent magnets

Normally used in measuring instruments.

Properties of the material of a permanent magnet :

(1)  It should have high retentivity so that it remains magnetised in the absence of the magnetising field.

(2)  It should have high saturation magnetisation.

(3)  It should have high coercivity so that it does not get demagnetised easily.

Note:Compared to soft iron, steel has got low retentivity. Even then steel is preferred for a permanent magnet as it has got high coercivity.

### Trasformer cores

As the materials used for making transformer cores are subjected to many cyclic changes per second, so they are preferred to have low hysteresis loss. Moreover magnetic field B should be large. As soft iron shows these properties, hence it is always preferred to develop transformer cores.

## Eddy current & its applications

Eddy Currents :
Eddy currents are the currents induced in the body of a conductor when the amount of magnetic   flux linked with it changes. The experimental concept was given by Focault and hence they are also named as Focault currents.

Special points:
(1) These currents are produced in metal bodies

(a)They are placed in a time varying magnetic  field .

(b)They move in a magnetic field such that their flux through them changes or they cut away magnetic field lines .

(2) These currents are produced only in closed path within the entire volume of metal body or surface area of metal body. Therefore their measurement is impossible.

(3) These “circulatory” currents are always produced in planes perpendicular to magnetic lines of force.

(4) The resistance of bulk conductor is usually low, eddy currents often have large magnitudes and heat up the conductor. That’s why these are sometimes undesirable.

(5) By ‘ Laminations ’ , slotting process, the resistance path for circulation of eddies increases, resulting in to weakening them and also reducing losses caused by them. Slots and laminations intercept the conducting paths and decrease the magnitude of eddy currents. That’s why a laminated metal core is always preferred to be used in an appliance like dynamo, transformer, choke will etc.

Special Examples on eddy currents

(1)If a metal piece and a stone are dropped from the same height near earth’s surface, then eddy currents are produced in the falling metal piece due to earth’s magnetic field which opposes its motion. So the metal piece falls with acceleration a < g. Whereas no eddies are produced in stone, so it will fall with acceleration due to gravity. So the stone will reach the earth earlier.

For any time interval : hmetal > Hnonmetal

For any given height   : tmetal > tnonmetal

(2)If a metallic plate is below an oscillating magnet, then magnet stops soon because eddy currents are produced in the plate which opposes the motion of magnet. This is the basis of electromagnetic damping.

(3)  If a bar magnet is falling vertically through the hollow region of a long vertical copper tube, then the magnetic flux linked with the copper tube (due to ‘non-uniform’ magnetic field of magnet) changes and eddy currents are generated in the body of the tube.
By Lenz’s law the eddy currents oppose the falling of the magnet which therefore experiences a retarding force .The retarding force increases with increasing velocity of the magnet and finally equals the weight of the magnet. The magnet then attains a constant final terminal velocity i.e. magnet ultimately falls with zero acceleration in the tube.

On heating the tube its resistance will increase and so the eddy currents will become feeble, resulting in an increase in the terminal velocity of the magnet.

Applications of eddy currents

(i)    Induction furnace (heating effect of eddy current)

(iii)  Electric brakes

(iv) Diathermy ( Strong 50 MHz A.C. passed through human body, also called deep heat treatment )

(v)  Induction motor

(vi) Car-speedometer

(vii)Energy meter

## Thomson Mass Spectrograph

Thomson Mass Spectrograph which is used to measure atomic masses of various isotopes in a gas :

Thomson mass spectrograph is used to measure atomic masses of various isotopes in a gas. This is done by measuring q/m of singly ionized positive ions of the gas. The positive ions are produced in the bulb at the left-hand side. These ions are accelerated towards cylindrical cathode C.

Some of the positive ions pass through the fine hole in the cathode. This fine ray of positive ions is subject to electric field E and magnetic field B and then allowed to strike a fluorescent screen or photographic plate placed just before the screen (not shown in figure). The positive ions produced near the anode are accelerated through a greater distance and thus have more kinetic energy and velocity. The different positive ions have different speeds. It can be shown that all positive ions having the same q/m, fall on the screen or photographic plate forming a parabolic trace. By changing the direction of B the other side of the parabola can be obtained.
It is found that separate isotopes forms separate parabola. Thus the number of parabolas (figure) given the number of isotopes in the gas taken in the bulb. Some ions after coming out of the cathode get neutralize and continue to move in a straight line. The impinge at the vertex of the parabola, forming a dark spot on the photographic plate.

The electric field and magnetic field are parallel to each other. However, the electric force and the magnetic force are perpendicular to each other. The deflection (upwards) due to the electric field alone as observed on the screen is .

Y = qELD/mu2

While the deflection (side ways) due to the magnetic field alone is

X = qBLD/mu

Eliminating u, we notice that when both E and B are present, then X – Y coordinates of the deflection are related by

$\displaystyle X^2 = \frac{B^2 L D}{E} (\frac{q}{m} ) Y$

For a given spectrograph B , L , D , E are constants , then

$\displaystyle X^2 = K (\frac{q}{m}) Y$

Note :

(1)   Thus all positive ions having charge to mass ratio (q/m) lie on a parabola. Higher is the velocity, lower is the value of Y and X. In principle only those positive ions for which velocity is infinite can reach the origin O.

(2)   Thus, infact, the trace does not extend upto origin O (vertex of the parabola). Since the highest velocity positive ions are those which originate near anode, the parabola’s lower end is due to high velocity ions, low velocity ions are far away from the vertex on the parabolic trace.

(3)   To determine m1/m2 ratio of isotopic masses, one draws a horizontal line on the parabolic trace (see figure). Thus Y is same for the two traces. Then the ratio m1/m2 is found to be (use X2 = K (q/m) Y).

$\displaystyle \frac{m_1}{m_2} = \frac{(AB)^2}{(CD)^2}$

where AB = 2X2 and CD = 2X1 in the figure. The heavier isotope lie on the inner parabolic trace while the lighter isotope is on the outer parabolic trace. The q/m is large for the outer parabola (m small) while q/m is small for the inner parabola. Thomson, using this spectrograph, discovered the isotopes of the neon.

Drawbacks:

(i) The resolving power of Thomson spectrograph is poor.

(ii) The parabolas are thick (diffused) as such it is difficult to accurately measure the distances AB and CD.

(iii) Since the positive ions are spread over a parabolic trace, the intensity is weak as such isotope having a little abundance may not be able to form a detectable parabolic trace.

(iv) If the positive ions before striking the screen (photographic plate) collide with atoms of the gas in the spectrograph tube, they will diffuse the parabolic trace and may also give rise to false parabolic traces.

(v) The relative abundance of the isotopes is estimated by intensity of the parabolic traces.

## Various Models for Structure of Atom

Dalton’s Theory:

(a)  Every material is composed of minute particles known as atom. Atom is indivisible i.e. it cannot be subdivided. It can neither be created nor be destroyed.

(b)  All atoms of same element are identical physically as well as chemically, whereas atoms of different elements are different in properties.

(c)  The atoms of different elements are made up of hydrogen atoms. (The radius of the heaviest atom is about 10 times that of hydrogen atom and its mass is about 250 times that of hydrogen.)

(d)The atom is stable and electrically neutral.

Thomson’s Atom Model :
(a)  The atom as a whole is electrically neutral because the positive charge present on the atom (sphere) is equal to the negative charge of electrons present in the sphere.

(b)  Atom is positively charged sphere of radius 10–10 m in which electron are embedded in between.

(c)  The positive charge and the whole mass of the atom is uniformly distributed throughout the sphere

Shortcomings of Thomson’s Model :

(i) The spectrum of atoms cannot be explained with the help of this model.

(ii) Scattering of α-particles cannot be explained with the help of this model.

Rutherford Atom Model :

Rutherford performed experiment of scattering of α-particles by thin gold foil and concluded:

(a)  Most of the a-particles went straight through the gold foil and produced flashes on the screen as if there were nothing inside gold foil. Thus the atom is hollow.

(b)  Few particles collided with the atoms of the foil which have scattered or deflected through considerable large angles. Few particles even turned back towards source itself.

(c)  The entire positive charge and almost whole mass of the atom is concentrated in small centre called nucleus.

(d)  The electrons could not deflected the path of a a-particles i.e. electrons are very light.

(e)  Electrons revolve round the nucleus in circular orbits.

So, Rutherford 1911, proposed a new type of model of the atom. According to this model, the positive charge of the atom, instead of being uniformly distributed throughout a sphere of atomic dimension is concentrated is a very small volume (less than 10–13 m in diameter) at its centre. The central core, now called nucleus, is surrounded by clouds of electron makes. The entire atom electrically neutral.

The scattering angle decreases with increasing impact parameter.

Bohr’s Theory of Hydrogen Atom :

Bohr’s theory of hydrogen atom is based on the following assumption :

1. Only these orbits are possible for which the orbital angular momentum of the electron is equal to an integral multiple of h/2π  ; where h is Plank  constant.
1. The electron moving in such allowed orbits does not radiate electromagnetic radiations. Thus the total energy of the electron revolving in any of the so many stationary orbits remains constant.
2. Electromagnetic radiations are emitted if an electron jumps from stationary orbit of higher energy E2 to another stationary orbit of lower energy E1. The frequency n of the emitted radiation is related by the equation.

Defects of Bohr Model:

(a)  This model could not explain the fine structure of spectral lines, Zeeman effect and Stark effect.

(b)  This model is valid only for single electron systems.

(c)  This model is based on circular orbits of electrons whereas in reality the orbits are elliptical.

(d)   Electron is presumed to revolve round the nucleus only whereas in reality it also rotates about its own axis.

(e)  This model could not explain the quantization condition of angular momentum (i.e. the classical and quantum theories were used simultaneously).

(f)  This model could not explain the intensity of spectral lines.

(g)  It could not explain the doublets obtained in the spectra of some of the atoms.